This invention relates in general to temperature controllers for heating and cooling systems, and more specifically to a method and apparatus for operating a thermostat to provide an automatic changeover between heating and cooling modes.
Thermostats for use with a building heating and cooling system are well known. A typical prior-art thermostat provides a mode switch having at least two positions for allowing a user to changeover manually between a heating mode, in which the thermostat controls the heating system; and a cooling mode, in which the thermostat controls the cooling system. Such thermostats generally have used a single setpoint temperature. Unfortunately, these thermostats require frequent user attention to the mode switch during temperate seasons such as Spring and Fall, in which cooling may be desired during the day, and heating at night.
In an attempt to automate the changeover between heating and cooling, manufacturers of prior-art thermostats have constructed xe2x80x9cautomatic-changeoverxe2x80x9d thermostats, which have used first and second setpoint temperatures, respectively, for heating and cooling. In such prior-art thermostats, the first and second setpoint temperatures are not independent of each other, because, in effect, both are active simultaneously. The first setpoint temperature is required to be less than the second setpoint temperature by a predetermined number of degrees, e.g., 4-5 degrees F., to prevent excessive cycling of the thermostat between heating and cooling due to a demand for heating causing the sensed room temperature to move into the cooling operational range, and vice versa. Unfortunately, without manual intervention, this type of prior-art thermostat forces the average room temperature when using heat to be at least 4-5 degrees F. cooler than the average room temperature when using cooling, which some people find uncomfortable.
Thus, what is needed is an automatic changeover thermostat in which the first and second setpoint temperatures can be set independently of each other, without concern for excessive cycling between heating and cooling. Such a thermostat preferably will allow the use of a single setpoint temperature for both heating and cooling, if desired, without requiring manual user intervention to select between the heating and cooling modes.